I used Nokia's fonts(including Pure Text) and found they are good, not the best ones.

Then I switch to cantarell, which is too wide comparing to other. Next, I dropped Ubuntu Family, then Pt Family, later Droid Family, then Linux Libertine Family.

The latest font I am using now is Ubuntu, yes, 2 days ago, I went back to Ubuntu, with 0.8.0 new release. Pretty and Bold shape. Although mono I would have Liberation Mono everywhere.